Julian Bianchi above also points to this as a key piece of data. I don't see conclusive evidence yet in casual browsing. Perhaps the question has been examined and answered empirically.
If there is little or no difference in branching ratios, that would admittedly be a strong piece of evidence against a whole category of cold fusion theories.
We are by no means first to ask this question. Here at SJ Byrnes' blog: http://sjbyrnes.com/cf/muons/
"Experimentally, there are tons of muon-catalyzed fusion experiments, but in my (cursory) search I have not found any papers that took the appropriate data to figure out whether or not this branch actually happens."
Unfortunately Byrnes is not even addressing a change in the usual branching ratios, that is:
- D+D → neutron + helium-3 (~50% of the time),
- D+D → proton + tritium (~50% of the time),
- D+D → helium-4 + a gamma-ray (0.0001% of the time)
But instead is concerned with what Byrnes calls the "spectator" branch, which might enable practical muon catalyzed fusion:
- D+D+muon → helium-4 + muon
So, in spite of the interesting discussion at the Byrnes blog, I will continue to browse.
See eg Chapter 4.2 of IMHO the best review on muon catalyzed fusion: